What Luvrbus said!. Take the old relay to a good parts store and try to match it up. It does not have to look exactly the same. You just care about the terminals functioning the same. Getting parts for your bus will often be like that. Parts clerks will ask about the vehicle, but that rarely is of any use. You have to match a part. They want to look it up in a catalogue by make and model, but these buses are not in their catalogues. Aside from which, things might have been altered over the years.

Something else we noticed... The "no charge" light on the dash is on, so just to rule it out, we swapped item 8 and item 9 (see below) and it kept the "no charge" light from coming on but our overall problem is still the same.

I'm sending you a photo of the driver's panel by email. That relay has nothing to do with starting as you can see.

When you start the engine and it quits soon do you have any air pressure? It sounds like the classic case of having the rear run switch turned off. If you haven't moved it it may be so badly corroded that it has failed open. Happened to me. I had to jump wire around it.

That relay doesn't have the same terminal layout as a cube relay so they won't work unless you rewire the whole thing. You will need the cube relay base and will need to make sure it will carry the required amps. The average cubes are 30-40 amps which should be enough for a starting circuit.

I think of solenoids as the ones like on starters and relays as the smaller ones like cube relays, but that isn't technically the correct definitions. They are all remote switches which covers all!

A cube relay will not replace the bus steel, round solenoids with large terminals because none of the large wires will connect. I suppose you could rewire the whole thing by using a cube relay socket but the wires are nowhere nearly as large on most.

That photo looks like the horn relay or stop light relay. As you can see in the photo there are only four of those in this panel. My 4107 start relay is in the back left panel above the engine and is a steel, round solenoid with large terminals

Oh my goodness!!! The engine run switch! I guess that was my first time with the classic case of that lol. This still hasn't solved my possible problem of the clicking noise that started this post. I had thought all this was related but maybe not being that it was just the engine switch.

Again the clicking noise will come from the left driver panel and I will loose power at the same time it makes noise.

Man thank you so much for helping. I still can't get over the engine switch haha.

The charging system will have a charging relay your bus is probably 24volt the charging relay will be 12 volt for a 24 volt 50D alternator if 12 volt it will be 6 volt you can buy the adapter to go from coil type relays to the cubes if you choose, check the field on the alternator when it shuts off and see if it is still magnetized

I understand the engine doesn't stop so feel the relays in the panel when clicking starts, it will be easy to identify it and you won't get any kind of shock.

Do you mean the toggle switch on the panel? I call that the engine run switch? I've had at least three of those old toggle switches fail on my two buses. Usually the spring inside fails or it corrodes and opens.

Interesting that the photo of that panel you posted is not the same as the one in my 4107 manual?? Yours is an actual photo of the panel and mine is a drawing without the wires?

8 and 9 are the only ones that I think you could hear, the others are probably too small to be heard. Or maybe 7 is sounding off for some reason?

The noise maker in mine was/is the Generator Magnetic Switch (9) which actually has nothing to do with the gen, it cuts off the blower motor if the gen isn't producing adequate power! ( would make the same sound.

These old elect systems get so changed around in conversions, especially the alarm systems, that they cause many very strange things to happen. Often the quickest way is just to wire around them.

I'm still suspicious of the rear elect panel, switches there catch a lot of crud from the engine and fail/rust.

You really don't want to wire around the charging relay when you start to lose power check the voltage on the alternator I bet it is very high loading the engine IMO, Bill's 4905 would do the same his is a 24 volt system and would produce 32+ volts slowing the engine down and had no power

His was a grounding problem the regulator will not regulate the voltage when it does not see a ground only took a week to find that out lol

What I wired around was the rear panel engine switches because they were so corroded they were causing problems. Sorry!

This didn't cut anything out of the circuits except those rear switches. I was afraid to try to install new ones and mess things up even more!!

I'm having another problem now, the VR is not getting the full 12V which also comes via the rear panel so I probably have another jumper wiring to do. That rear panel on mine has no cover so the whole thing is a mess.

Grounding of the VR is, indeed, a problem. The PO had added an additional ground wire to my VR at some time.

Yea my rear panel is the same way, it doesn't have a cover on it. Lots of dirty wires. I'm rerunning my tail lights, signals, brake lights, etc, and also installing reverse lights to an unused switch. By the way, where can I get those dash switches? Some of mine need replacing.